This invention relates generally to the field of blow molding and more particularly to an improved method and apparatus for blow molding articles with deeply recessed edges.
Conventional blow molding apparatus includes an extrusion head for producing an downwardly extending tubular parison and mold halves that are disposed on opposite sides of the parison in the open position of the mold. The mold halves are closed on the parison so as to pinch the lower edge of the parison closed and a blow pin assembly is usually inserted in the upper end of the mold to form the upper end of the parison into the neck and blow the parison into conformity with the mold cavity.
If the article being formed has one or more deeply recessed edges at either its top or bottom ends, and the parison is of the conventional shape at the time blow air is introduced, there is little likelihood that enough plastic will be extended into the recessed edge to form the edge of the desired strength and thickness. It is an object of the present invention, therefore, to provide an improved method and apparatus wherein the parison is closer to the recessed edge or edges before the parison is expanded into conformity with the mold cavity.
In a search of the prior art, U.S. Pat. Nos. 3,050,773, 4,092,392, 4,170,623 were found disclosing sectionalized mold halves, principally for the purpose of forming side wall extensions on containers. An article in Plastics Engineering, October 1982, page 21, discloses the concept of splitting a mold to control wall thickness. However, none of these references disclose the method and apparatus of this invention.